The sharp turns in currency and other markets have led some observers to wonder if greater volatility may be an unintended consequence of an effort to reduce banks’ balance-sheet risk.

Robert Savage, chief executive of the currency hedge fund CCtrack Solutions LLC and a former Goldman Sachs Group Inc. executive, said when volatility increases to a point that high-frequency trading programs lose money by making markets, “they just shut down.”

Bank trading desks staffed by employees would have kept the selloff from escalating to the degree it did, he said. “You would find out who was selling, if there was any news,” Mr. Savage said. “In the old days, if there was no fundamental reason to sell, you wouldn’t sell.”